Hydroxy-amino thermally cured undercoat for 193 NM lithography

ABSTRACT

The present invention is directed to a thermally curable polymer composition, and a photolithographic substrate coated therewith, the composition comprising a hydroxyl-containing polymer, an amino cross-linking agent and a thermal acid generator. The thermally curable polymer composition may be dissolved in a solvent and used as an undercoat layer in deep UV lithography.

FIELD OF THE INVENTION

The present invention relates to deep UV lithography used insemiconductor manufacturing and more particularly to undercoat layersfor chemically amplified bilayer resist systems.

BACKGROUND TO THE INVENTION

Integrated circuit production relies on the use of photolithographicprocesses to define the active elements and interconnecting structureson microelectronic devices. Until recently, g-line (436 nm) and I-line(365 nm) wavelengths of light have been used for the bulk ofmicrolithographic applications. However, in order to achieve smallerdimensions of resolution, the wavelength of light used formicrolithography in semiconductor manufacturing has been reduced intothe deep UV regions of 256 nm and 193 nm. The problem with using deep UVwavelengths is that resists used at the higher wavelengths were tooabsorbent and insensitive. Thus, in order to utilize deep UV lightwavelengths, new resist materials with low optical absorption andenhanced sensitivities were needed.

Chemically amplified resist materials have recently been developedthrough the use of acid-labile polymers in order to meet theabove-mentioned criteria. They have shown great promise in increasingresolution. However, chemically amplified resist systems have manyshortcomings. One problem is standing wave effects, which occur whenmonochromatic deep UV light is reflected off the surface of a reflectivesubstrate during exposure. The formation of standing waves in the resistreduces resolution and causes linewidth variations. For example,standing waves in a positive resist have a tendency to result in a footat the resist/substrate interface reducing the resolution of the resist.

In addition, chemically amplified resist profiles and resolution maychange due to substrate poisoning. Particularly, this effect occurs whenthe substrate has a nitride layer. It is believed that the N—H bond inthe nitride film deactivates the acid at the nitride/resist interface.For a positive resist, this results in an insoluble area, and eitherresist scumming, or a foot at the resist/substrate interface.

Furthermore, lithographic aspect ratios require the chemically amplifiedresist layer be thin, e.g., about 0.5 μm, to print sub 0.18 μm features.This in turn requires the resist to have excellent plasma etchresistance such that resist image features can be transferred down intothe underlying substrate. However, in order to decrease absorbance ofthe chemically amplified resist, aromatic groups, such as those innovolaks had to be removed, which in turn decreased the etch resistance.

Utilizing an underlayer or undercoat film that is placed on thesubstrate before the chemical amplified film is applied can reduce theabove-mentioned problems. The undercoat absorbs most of the deep UVlight attenuating standing wave effects. In addition, the undercoatprevents deactivation of the acid catalyst at the resist/substrateinterface. Furthermore, the undercoat layer can contain some aromaticgroups to provide etch resistance.

In the typical bilayer resist process, the undercoat layer is applied onthe substrate. The chemically amplified resist is then applied on theundercoat layer, exposed to deep UV light and developed to form imagesin the chemically amplified resist topcoat. The bilayer resist system isthen placed in an oxygen plasma etch environment to etch the undercoatin the areas where the chemically amplified resist has been removed bythe development. The chemically amplified resist in a bilayer systemtypically contains silicon and is thus able to withstand oxygen plasmaetching. After the bottom layer is etched, the resist system can be usedfor subsequent processing such as non-oxygen plasma etch chemistry whichremoves the underlying substrate.

Even though the undercoat attenuates standing waves and substratepoisoning, it poses other problems. First, some undercoat layers aresoluble to the chemical amplified resist solvent component. If there isintermixing between the top and undercoat layers, the resolution andsensitivity of the top resist layer will be detrimentally affected.

In addition, if there is a large difference in the index of refractionbetween the chemical amplified resist and the undercoat layer, lightwill reflect off the undercoat layer causing standing wave effects inthe resist. Thus, the index of refraction between the two layers must bematched to minimize reflectivity effects.

Another problem with undercoating layers is that they are sometimes tooabsorbent because of incorporation of aromatic groups. Somesemiconductor manufacturing deep UV exposure tools utilize the samewavelength of light to both expose the resist and to align the exposuremask to the layer below the resist. If the undercoat layer is tooabsorbent, the reflected light needed for alignment is too attenuated tobe useful. However, if the undercoat layer is not absorbent enough,standing waves may occur. A formulator must balance these competingobjectives.

In addition, some undercoats have very poor plasma etch resistance toplasma chemistry. The etch resistance of the undercoat should becomparable to the etch rate of novolak resins in order to becommercially viable.

Furthermore, some undercoat layers require UV exposure in order to formcross-links before the radiation sensitive resist topcoat layer can beapplied. The problem with UV cross-linking undercoat layers is that theyrequire long exposure times to form sufficient cross-links. The longexposure times severely constrain throughput and add to the cost ofproducing integrated circuits. The UV tools also do not provide uniformexposure so that some areas of the undercoat layer may be cross-linkedmore than other areas of the undercoat layer. In addition, UVcross-linking exposure tools are very expensive and are not included inmost resist coating tools because of expense and space limitations.

Some undercoat layers are cross-linked by heating. However, the problemwith these undercoat layers is that they require high curingtemperatures and long curing times before the top layer can be applied.In order to be commercially useful, undercoat layers should be curableat temperatures below 250° C. and for a time less than 180 seconds.After curing, the undercoat should have a high glass transitiontemperature to withstand subsequent high temperature processing.

Therefore, it is an object of the present invention to provide athermally curable polymer composition that is useful for an undercoatlayer in deep UV lithography. Another object of the present invention isto provide an undercoat layer, which is cured at temperatures less thanabout 250° C. and for a time less than about 3 minutes. It is a furtherobject of this invention to provide an undercoat layer which isinsoluble to the top resist's solvent system, minimizes reflectivityeffects, and has an etch rate comparable to novolaks.

Other and further objects, advantages and features of the presentinvention shall become apparent as described below.

SUMMARY OF THE INVENTION

The present invention is directed to a thermally curable polymercomposition comprising a hydroxyl-containing polymer, an aminocross-linking agent and a thermal acid generator. The thermally curablepolymer composition may be dissolved in a solvent and used as anundercoat layer in deep UV lithography.

In addition, the present invention also relates to a photolithographiccoated substrate comprising: a substrate, a thermally cured undercoatcomposition on the substrate, and a radiation-sensitive resist topcoaton the thermally cured undercoat composition. Furthermore, the presentinvention further relates to a process for using the photolithographiccoated substrate for the production of relief structures.

DETAILED DESCRIPTION AND EMBODIMENTS

This invention relates to a thermally curable polymer composition, whichmay be used for forming an undercoat layer in deep UV lithography. Thethermally curable polymer composition comprises a hydroxyl-containingpolymer, an amino cross-linking agent and a thermal acid generator and.When the composition is heated, the thermal acid generator protonatesthe polyfunctional amino cross-linking agent resulting in a very strongelectrophillic group. This group reacts with a hydroxyl group on thehydroxyl-containing polymer forming a cured cross-linked polymer matrix.

Any suitable amino cross-linking agent may be used in the presentapplication such as methylolated and/or methylolated and etherifiedmelamines, methylolated and/or methylolated and etherified guanaminesand the like. The preferred amino cross-linking agents have the generalformula:

wherein Y is NR₅R₆ or a substituted or unsubstituted aryl or alkylgroup; and R₁ to R₆ are independently a hydrogen or a group of theformula —CH₂OH or —CH₂OR₁₇ wherein R₁₇ is a alkyl group of about 1 to 8carbons.

Examples of suitable melamine cross-linking agents aremethoxyaklylmelamines such as hexamethoxymethylmelamine,trimethoxymethylmelamine, hexamethoxyethylmelamine,tetramethoxyethylmelamine, hexamethoxypropylmelamine,pentamethoxypropylmelamine, and the like. The preferred melaminecross-linking agent is hexamethoxymethylmelamine.

The thermal acid generator of the present invention has the generalformula:

where R₇ is a substituted or unsubstituted alkyl, cycloalkyl or aromaticgroup wherein the substituted group is a halogen, alkoxy, aromatic,nitro or amino group; and R₈ to R₁₂ are independently selected fromhydrogen, linear or branched C₁ to C₄ alkyl, alkoxy, amino, alkylamino,aryl, alkenyl, halogen, acyloxy, cycloalkyl, or annulated cycloalkyl,aromatic or heterocyclic. More preferable thermal acid generators arecyclohexyl p-toluenesulfonate, menthyl p-toluenesulfonate and cyclohexyl2,4,6-triisopropylbenzenesulfonate.

Annulated means that the cycloalkyl, aromatic or heterocyclic ring isconnected onto the benzene ring of the thermal acid generator such as,for example, the annulated aromatic shown below

The preferred thermal acid generators are cyclohexyl p-toluenesulfonate,menthyl p-toluenesulfonate, bornyl p-toluenesulfonate, cyclohexyltriisopropylbenzenesulfonate, cyclohexyl 4-methoxybenzene sulfonate.

The thermal acid generators described above should not be consideredphotoacid generators. Any sensitivity that the thermal acid generatorswould have to UV light should be very poor, and they cannot practicallybe used in photolithography as a photoacid generator.

The thermally curable polymer composition also comprises ahydroxyl-containing polymer. Any suitable hydroxyl-containing polymermay be used such as polymers comprising monomer units of cyclohexanol, ahydroxystyrene, hydroxyalkyl acrylate or methacrylate, hydroxycycloalkylacrylate or methacrylate, arylalkyl alcohols, allyl alcohol and thelike. This invention also contemplates copolymers, terpolymers, and thelike of the foregoing named polymers. In addition, polymers containingnovolaks may also be used.

Preferably, polymers comprising monomer units of cyclohexanol, ahydroxystyrene hydroxyalkyl acrylate or methacrylate, arylalkyl alcoholsand hydroxycycloalkyl acrylate or methacrylate have a number averagemolecular weight of about 9000 to 38,000, more preferably 14,000 to30,000 and even more preferably about 18,000 to 22,000.

In addition, the thermally curable polymer composition may also furthercomprise monomer units of cycloaliphatic esters of acrylic ormethacrylic acid. Suitable examples of monomer units of cycloaliphaticesters of acrylic or methacrylic acid are cyclohexyl acrylate ormethacrylate, 4-tert-butylcyclohexyl acrylate or methacrylate andisobornyl acrylate or methacrylate, adamantyl acrylates andmethacrylates, dicyclopentenyl acrylates and methacrylates,2-(dicylcopenteneyloxy)ethyl acrylates and methacrylates and the like.The preferred monomer units of cycloaliphatic ester of acrylic ormethacrylic acid are isobornyl acrylate or methacrylate.

Furthermore, the hydroxyl-containing polymer may further comprisearomatic monomer units, preferably styrene or biphenyl acrylate ormethacrylate.

Examples of suitable hydroxyalkyl acrylate or methacrylates monomerunits are hydroxymethyl acrylate or methacrylate, 2-hydroxyethylacrylate or methacrylate, 3-hydroxypropyl acrylate or methacrylate,4-hydroxybutyl acrylate or methacrylate, 5-hydroxypentyl acrylate ormethacrylate, and 6-hydroxyhexyl acrylate or methacrylate and the like.Preferably, the hydroxyalkyl acrylate or methacrylate monomer unitscontains primary hydroxyl groups, although secondary and tertiaryalcohol groups or mixtures of primary and secondary or primary,secondary and tertiary alcohol groups may be used. Suitable examples ofsecondary alcohols are 2-hydroxy-2-methylethyl acrylate or methacrylate,3-hydroxy-3-methypropyl acrylate, 4-hydroxy-4-methylbutyl acrylate ormethacrylate, 5-hydroxy-5-methyl propyl acrylate or methacrylate, andthe like. The preferred hydroxyalkyl acrylate or methacrylate is2-hydroxyethyl acrylate or methacrylate.

Suitable examples of arylalkyl alcohol monomer units are benzyl alcohol,4-methyl-benzyl alcohol, 4-ethyl-benzyl alcohol, cumyl alcohol,alpha-methyl benzyl alcohol, 2-phenyl-1-ethanol, 3-phenyl-1-propanol,and 1-naphthyl methanol.

Other preferred copolymers useful in the thermally curable polymercomposition are a copolymer of styrene and allyl alcohol monomer unitswith a weight average molecular weight of about 2000 to 20,000,preferably 2000 to 10,000; and a copolymer of hydroxystyrene and acycloaliphatic esters of acrylic or methacrylic acid monomer units witha number average molecular weights of about 9000 to 38,000, preferablyabout 14,000 to 30,000, more preferably about 18,000 to 22,000.

The thermally curable polymer composition preferably contains about 75to 95 wt. %, and more preferably about 82 to 95 wt. % of hydroxylcontaining polymer. The amount of the amino cross-linking agent in thethermally curable polymer composition is preferably about 3 to 20 wt. %and more preferably about 5 to 15 wt. %. The amount of the thermal acidgenerator in the thermally curable polymer composition is preferablyabout 0.5 to 5 wt. % and more preferably about 1.5 to 3.5 wt. %.

The thermally curable polymer composition of the present inventionshould not begin significant cross-linking until it reaches atemperature of about 50° C. Significant cross-linking below 50° C. maylead to gel formation at room temperature, which will reduce its shelflife. Gel formation results in non-uniform coatings and linewidthvariations across the substrate when the thermally curable polymercomposition is used as an undercoat layer in microlithography.

The more preferable polymers of the present invention comprise polymerswith the following monomer units:

wherein R₁₅ and R₁₆ are independently selected from hydrogen or methyl.

Polymer 1 comprises about 40 to 75 mole % of isobornyl acrylate ormethacrylate monomer units and about 25 to 60 mole % of hydroxystyrenemonomer units.

Polymer 2 comprises about 39 to 60 mole % of styrene monomer units andabout 40 to 61 mole % of allyl alcohol monomer units.

Another preferable polymer (polymer 3) is a copolymer of biphenylacrylate or methacrylate and hydroxyethyl acrylate or methacrylate. Theamount of biphenyl acrylate or methacrylate is about 50 to 90 mole % andthe amount of hydroxyethyl acrylate or methacrylate is about 10 to 50mole %.

The polymerization of the polymers described above may be carried out byany suitable polymerization process such as free radical polymerization.The number average molecular weight of Polymers 1 and 3 are about 9,000to 38,000, preferably about 14,000 to 20,000 and more preferable about18,000 to 22,000. The weight average molecular weight of polymer 2 isabout 2,000 to 20,000, preferably about 2000 to 10,000.

The present invention also relates to a photolithographic coatedsubstrate comprising: a substrate, a thermally cured undercoatcomposition on the substrate, and a radiation-sensitive resist topcoaton the thermally cured undercoat composition. The thermally curedundercoat composition comprises the thermally curable polymercomposition that comprises a hydroxyl-containing polymer, an aminocross-linking agent and a thermal acid generator which has been heatedto form a cross-linked matrix. Any of the polymers described above maybe used as the hydroxyl-containing polymer. Preferably, thehydroxyl-containing polymer is selected from Polymers 1 or 2.

The present invention further relates to a process for using thephotolithographic coated substrate for the production of reliefstructures comprising the steps of: providing the photolithographiccoated substrate, imagewise exposing the radiation-sensitive resisttopcoat to actinic radiation; and forming a resist image by developingthe radiation-sensitive resist topcoat with a developer to form openareas in the radiation-sensitive resist topcoat. In addition, thethermally cured undercoat composition may be removed in the open areasof the developed radiation-sensitive resist topcoat by any suitableprocess such as oxygen plasma etching to form an image in the thermallycured undercoat composition.

One advantage of the thermally curable polymer composition is that itmay be cured at a temperature of less than about 250° C. and for a timeless than about 180 seconds. This make it particularly useful as anundercoat layer for a resist system where temperature and timeconstraints are important for commercial viability. Preferably, thethermally curable polymer composition is cured at temperatures between150 to 250° C. and more preferably between temperatures of 180 to 220°C. The preferably curable times are from about 30 to 180 seconds andmore preferably from about 60 to 120 seconds.

Both the undercoat and the radiation-sensitive compositions areuniformly applied to a substrate by known coating methods. Thecompositions are solubilized in an organic solvent and the coating s maybe applied by spin-coating, dipping, knife coating, lamination,brushing, spraying, and reverse-roll coating. The coating thicknessrange generally covers values of about 0.1 to more than 10 μm and morepreferably from about 0.1 to 1.5 um for the radiation-sensitive resistand about 0.3 to 3.0 um for the undercoat layer. After the coatingoperation, the solvent is generally removed by curing or drying.

Suitable solvents for both the undercoat and top radiation-sensitivecompositions include ketones, ethers and esters, such as methyl ethylketone, methyl isobutyl ketone, 2-heptanone, cyclopentanone,cyclehexanone, 2-methoxy-1-propylene acetate, 2-methoxyethanol,2-ethoxyethanol, 2-ethoxyethyl acetate, 1-methoxy-2-propyl acetate,1,2-dimethoxy ethane ethyl acetate, cellosolve acetate, propylene glycolmonoethyl ether acetate, propylene glycol methyl ether acetate, methyllactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, methyl3-methoxypropionate, ethyl 3-methoxypropionate, N-methyl-2-pyrrolidone,1,4-dioxane, ethylene glycol monoisopropyl ether, diethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, diethylene glycoldimethyl ether, and the like.

The radiation-sensitive resist topcoat of the present invention may beany suitable radiation-sensitive resist. It is typically a chemicallyamplified resist sensitive to radiation in the deep UV region such asthose discussed in U.S. Pat. Nos. 5,492,793 and 5,747,622. Preferably,for a bilayer resist system, the radiation-sensitive resist will containsilicon to protect it from oxygen plasma etching. A preferable radiationsensitive resist topcoat comprises a polymer comprising the followingmonomer units:

wherein R₁₃ is methyl or hydroxyethyl, R₁₄ is hydrogen, methyl orCH₂CO₂CH₃, and R₁₅ and R₁₆ are hydrogen or methyl, with each choice madeindependently.

The radiation-sensitive resist will also contain a photoacid generating(PAG) compound. The PAG compounds may be of any suitable type such assulfonium or iodonium salts, nitrobenzyl esters, imidosulfonates estersand the like. Typically, the PAG will be present in an amount of about 1to 10% based on the weight of the polymer.

For the production of relief structures, the radiation-sensitive resistis imagewise exposed to actinic radiation. The term ‘imagewise’ exposureincludes both exposure through a photomask containing a predeterminedpattern, exposure by means of a computer controlled laser beam which ismoved over the surface of the coated substrate, exposure by means ofcomputer-controlled electron beams, and exposure by means of X-rays orUV rays through a corresponding mask. The imagewise exposure generatesacid in the exposed regions of the resist which cleaves the acid labilegroups resulting in a polymer which is aqueous soluble. Typically, afterimagewise exposure, the chemically amplified resist will be subjected toa post exposure heating treatment that virtually completes the reactionof the photoacid generator with the acid labile groups.

After imagewise exposure and any heat treatment of the material, theexposed areas of the top radiation-sensitive resist are typicallyremoved by dissolution in a aqueous developer. The choice of theparticular developer depends on the type of photoresist; in particularon the nature of the polymer resin or the photolysis products generated.The developer can comprise aqueous solutions of bases to which organicsolvents or mixtures thereof may have been added. Particularly preferreddevelopers are aqueous alkaline solutions. These include, for example,aqueous solutions of alkali metal silicates, phosphates, hydroxides andcarbonates, but in particular of tetra alkylammonium hydroxides, andmore preferably tetramethylammonium hydroxide (TMAH). If desired,relatively small amounts of wetting agents and/or organic solvents canalso be added to these solutions.

The radiation-sensitive resist used for the bilayer process describedabove will typically contain silicon or have silicon incorporated intothe resist after development. After images are formed in theradiation-sensitive resist, the substrate will be placed in anplasma-etching environment comprising oxygen so that the underlayercoating will be removed. The silicon incorporated in theradiation-sensitive resist forms silicon dioxide when exposed to anoxygen plasma and protects it from being etched so that reliefstructures can be formed in the undercoat layer.

After the oxygen plasma step, the substrate carrying the bilayer reliefstructure is generally subjected to at least one further treatment stepwhich changes the substrate in areas not covered by the bilayer coating.Typically, this can be implantation of a dopant, deposition of anothermaterial on the substrate or an etching of the substrate. This isusually followed by the removal of the resist coating from the substratetypically by a fluorine/oxygen plasma etch.

It was surprising and unexpected that the present thermally curablepolymer composition worked well as an undercoat layer for lithographywith the amino cross-linking agent. There was a concern that thenitrogen bonds in the cross-linking group would deactivate the acid in apositive radiation sensitive resist resulting in an insoluble area, andeither resist scumming or a foot at the resist/undercoat interface.However, the following examples showed that the resolution of the resistwas excellent and that there was no scumming or foot at theresist/undercoat interface.

This invention is explained below in further detail with references toexamples, which are not by way of limitation, but by way ofillustration.

EXAMPLE 1 Synthesis Procedure for Polymer 1

In a 100 ml three-necked round bottom flask equipped with a magneticstir bar, addition funnel, condenser, and nitrogen inlet-outlet wasadded a mixture of 21.0 g of isobomyl methacrylate, 9.0 g of4-hydroxystyrene 30 ml of tetrahydrofuran (THF) and 0.45 g of2,2′-azobis(2-methylbutyronitrile). The mixture was heated to 65° C. andstirred for 18 hours. The solution was precipitated by addition to 1liter of hexanes, and the precipitate was filtered. The solid was driedfor 1 hour under a water aspirator vacuum, subsequently dissolved in 80ml of THF and reprecipitated in 1 liter of hexanes. The precipitate wasfiltered, and the solid dried at 4 mbar for 24 hours. The yield ofpolymer was between 77-80%. The above polymer was suspended in a mixtureof 70 ml isoproponal, 50 ml THF and 29.5 ml of NH₄OH under a nitrogenatmosphere. After refluxing overnight, the solution was cooled andprecipitated by adding 1 liter of water. The suspension was filtered andwashed with 50 ml of water and 50 ml of hexanes. The solid wasredissolved in THF and precipitated by the addition of 1.2 liter ofhexanes. The precipitate was filtered according to the above procedure.The solid was dried at 4 mbar for 24 hours. Molecular weights andmolecular weight distributions were measured using a Waters Corp. liquidchromatograph. The number average molecular weight was 25,923 and thepolydispersity (Mw/Mn) was 2.80. Thermal decomposition measurements(TGA) were performed using a Perkin-Elmer thermal gravimetric analyzer(TGA-7) giving a weight loss of 50% between 260-380° C. The structureand composition of polymers was analyzed using a Bruker 250 MHzNMR-spectrometer. The mole % of isobornyl methacrylate was 60% and themole % of hydroxystyrene was 40%.

EXAMPLE 2 Thermally Curable Polymer Composition Using Polymer 1

A 15% by weight thermally curable polymer composition was formulated bycombining 2.18 g of Polymer 1 from Example 1 above, 0.3 g ofhexamethoxymethylmelamine and 0.8 g of cyclohexyl p-toluenesulfonate in17 g of propylene glycol methyl ether acetate (PGMEA). The mixture wasrolled overnight, and the undercoat solution was filtered twice througha 0.1 μm Teflon filter.

EXAMPLE 3 Thermally Curable Polymer Composition Using Polymer 2

A 15% by weight thermally curable polymer composition was formulated bycombining 2.18 g of Polymer 2 obtained from Scientific Polymer Products,Inc. (60 mole % styrene and 40 mole % allyl alcohol), 0.3 g ofhexamethoxymethylmelamine and 0.8 g of cyclohexyl p-toluenesulfonate in17 g of propylene glycol methyl ether acetate (PGMEA). The mixture wasrolled overnight, and the undercoat solution was filtered twice througha 0.1 μm filter.

EXAMPLE 4 Preparation of Bilayer Resist

A silicon wafer was spin coated with the formulation of Example 1 andbaked at 200° C. for 1 min to yield a 0.50 μm thick film. Aradiation-sensitive resist topcoat was spin coated over the undercoatlayer and baked at 100° C. for 1 min to yield a 0.25 μm thick film. Theradiation-sensitive resist topcoat was a chemically amplified resistsystem comprising a terpolymer of tetrahydropyranylmethacrylate/methylmethacrylate/methacryloxypropyl tris(trimethoxy) silane, atriphenylsulfonium-triflate PAG, a triphenylimidole base compound andPGMEA solvent. The coated wafer was then exposed using an ISI 248 nmwavelength stepper. The wafer was post exposure baked at 100° C. for 1min and developed for 30 sec in 0.262 N aqueous TMAH. The wafer was spundry and the image was analyzed by scanning electron microscopy (SEM).The SEM's showed that there was no scumming or foot at theresist/undercoat interface, no standing waves, and no intermixing of theundercoat and the imaging layer. The bilayer resolution was excellentand could resolve features as small as 0.14 μm in a dense line structureand 0.12 um for an isolated line structure. In addition, the glasstransition temperature of the undercoat was greater than 250° C., whichshows that it can withstand subsequent high temperature processing.Furthermore, the oxygen plasma etch rate of the undercoat was within 15%of the etch rate of novolaks.

EXAMPLES 5-12 Preparation and Lithographic Results of Bilayer Resist

Table 1 below shows the lithographic results of different formulationsof polymer 1 in Example 2 with an amino cross-linking agent(hexamethoxymethylmelamine) and a thermal acid generator (cyclohexylp-toluenesulfonate). The formulation and lithographic procedures are thesame as Examples 2 and 4.

TABLE 1 Cross-linking Thermal Acid Resolution Resolution Polymer 1 AgentGenerator PGMEA Dense Isolated Example (grams) (grams) (grams) (grams)lines (um) Lines (um) 5 2.75 0.15 0.11 17 0.14 0.13 6 2.60 0.30 0.11 170.14 0.13 7 2.70 0.23 0.08 17 0.14 0.12 8 2.81 0.15 0.05 17 0.14 0.13 92.41 0.27 0.04 15.4 0.14 0.12 10 3.71 0.68 0.11 25.5 0.15 0.13 11 3.940.45 0.11 25.5 0.14 0.12 12 4.16 0.23 0.11 25.5 0.15 0.13

SEM's showed that there were no scumming or foot at the resist/undercoatinterface, standing waves, and no intermixing of the undercoat and theimaging layer.

EXAMPLES 13-14 Preparation and Lithographic Results of Bilayer Resist

Table 2 below the lithographic results of two copolymers ofhydroxystyrene and isobornyl methacrylate formulated with the aminocross-linking agent and thermal acid generator described in Examples 5through 12. The polymer in example 13 contains 55 mole % hydroxystyreneand 45 mole % isobomyl methacrylate. The polymer in example 14 contains25 mole % hydroxystyrene and 75 mole % isobomyl methacrylate.

TABLE 2 Cross-linking Thermal Acid Resolution Resolution Polymer AgentGenerator PGMEA Dense Isolated Example (grams) (grams) (grams) (grams)lines (um) Lines (um) 13 3.84 0.53 0.13 25.5 0.15 0.13 14 3.84 0.53 0.1325.5 0.15 0.13

SEM's showed that there were no scumming or foot at the resist/undercoatinterface, no standing waves, and no intermixing of the undercoat andthe imaging layer.

The foregoing is illustrative of the present invention and is notconstrued as limiting thereof. The invention is defined by the followingclaims with equivalents of the claims to be included therein.

What is claimed is:
 1. A thermally curable polymer compositioncomprising a hydroxyl-containing polymer, an amino cross-linking agentand a thermal acid generator, wherein said hydroxyl-containing polymercomprises a polymer selected from the group consisting of: (a) ahydroxyl-containing polymer comprising a monomeric unit of allyl alcoholand having a polymer weight average molecular weight of 2,000 to 20,000,and (b) a hydroxyl-containing polymer comprising monomeric units of ahydroxystyrene and isobornyl acrylate or isobornyl methacrylate andhaving a polymer number average molecular weight of 14,000 to 30,000;and said amino cross-linking agent has the general formula:

wherein Y is selected from the group consisting of NR₅R₆, andsubstituted or unsubstituted aryl or alkyl group, and R₁ to R₆ areindependently selected from the group consisting of —CH₂OH and CH₂OR₁₇where R₁₇ is a alkyl group of about 1 to 8 carbons.
 2. The compositionof claim 1 wherein the thermal acid generator has the general structure:

where R₇ is a substituted or unsubstituted alkyl, cycloalkyl or aromaticgroup wherein the substituted group is a halogen, alkoxy, aromatic,nitro or amino group; and R₈ to R₁₂ are independently hydrogen, linearor branched C₁ to C₄ alkyl, alkoxy, amino, alkylamino, aryl, alkenyl,halogen, acyloxy, cycloalkyl, or annulated cycloalkyl, aromatic orheterocyclic groups.
 3. The composition of claim 1 wherein thehydroxyl-containing polymer comprises the following monomeric units:

wherein R₁₅ and R₁₆ are independently selected from the group consistingof a hydrogen and methyl.
 4. The composition of claim 3 wherein the mole% of monomer unit (A) is about 25 to 60 mole % and the mole % of monomer(B) is about 40 to 75 mole %.
 5. The composition of claim 1 wherein thehydroxyl-containing polymer comprises the following monomer units:


6. The composition of claim 5 wherein the mole % of momomer (C) is about39 to 60 mole % and the mole % of monomer (D) is about 40 to 61 mole %.7. The composition of claim 2 wherein the thermal acid generator isselected from the group consisting of cyclohexyl p-toluenesulfonate,menthyl p-toluenesulfonate, bornyl p-toluenesulfonate, cyclohexyltriisopropylbenzenesulfonate, and cyclohexyl 4-methoxybenzenesulfonate.8. A thermally curable polymer composition comprising ahydroxyl-containing polymer, an amino cross-linking agent and a thermalacid generator, wherein said hydroxyl-containing polymer comprises: ahydroxyl-containing polymer comprising a monomeric unit of allyl alcoholand having a polymer weight average molecular weight of 2,000 to 20,000,and said amino cross-linking agent has the general formula:

wherein Y is selected from the group consisting of NR₅R₆, and asubstituted or unsubstituted aryl or alkyl group, and R₁ to R₆ areindependently selected from the group consisting of —CH₂OH and CH₂OR₁₇where R₁₇ is a alkyl group of about 1 to 8 carbons.
 9. The compositionof claim 8 wherein the thermal acid generator has the general structure:

where R₇ is a substituted or unsubstituted alkyl, cycloalkyl or aromaticgroup wherein the substituted group is a halogen, alkoxy, aromatic,nitro or amino group; and R₈ to R₁₂ are independently hydrogen, linearor branched C₁ to C₄ alkyl, alkoxy, amino, alkylamino, aryl, alkenyl,halogen, acyloxy, cycloalkyl, or annulated cycloalkyl, aromatic orheterocyclic groups.
 10. The composition of claim 9 wherein the thermalacid generator is selected from the group consisting of: cyclohexylp-toluenesulfonate, menthyl p-toluenesulfonate, bornylp-toluenesulfonate, cyclohexyl triisopropylbenzenesulfonate, andcyclohexyl 4-methoxybenzenesulfonate.
 11. A thermally curable polymercomposition comprising a hydroxyl-containing polymer, an aminocross-linking agent and a thermal acid generator , wherein saidhydroxyl-containing polymer comprises: a hydroxyl-containing polymercomprising monomeric units of a hydroxystyrene and isobornyl acrylate orisobornyl methacrylate and having a polymer number average molecularweight of 14,000 to 30,000; and said amino cross-linking agent has thegeneral formula:

wherein Y is selected from the group consisting of NR₅R₆, andsubstituted or unsubstituted aryl or alkyl group, and R₁ to R₆ areindependently selected from the group consisting of —CH₂OH and CH₂OR₁₇where R₁₇ is a alkyl group of about 1 to 8 carbons.
 12. The compositionof claim 11 wherein the thermal acid generator has the generalstructure:

where R₇ is a substituted or unsubstituted alkyl, cycloalkyl or aromaticgroup wherein the substituted group is a halogen, alkoxy, aromatic,nitro or amino group; and R₈ to R₁₂ are independently hydrogen, linearor branched C₁ to C₄ alkyl, alkoxy, amino, alkylamino, aryl, alkenyl,halogen, acyloxy, cycloalkyl, or annulated cycloalkyl, aromatic orheterocyclic groups.
 13. The composition of claim 12 wherein the thermalacid generator is selected from the group consisting of: cyclohexylp-toluenesulfonate, menthyl p-toluenesulfonate, bornylp-toluenesulfonate, cyclohexyl triisopropylbenzenesulfonate, andcyclohexyl 4-methoxybenzenesulfonate.